Color stabilization of white petroleum oils



Patented Nov. 18, 1941 COLOR STABILIZATION F WHITE PETRO- LEUMI OILS Henry C. Paulsen, Elizabeth, N. .L, assignor to I Standard Oil Development Company, a corporation of Delaware No Drawing.

Application May 4, 1940,

Serial N0. 333,339

Claims.

This invention relates to method for stabilizing the color of white or substantially colorless light petroleum distillate products, such as highly refined gasoline, naphthas, and kerosene, purified to the extent that they are substantially free of corrosive substances.

It is known to those skilled in the art that even highly refined petroleum products often contain gum and color-forming bodies which, under the accelerating photo-chemical action of sunlight, cause these products to become degraded in color, cloudy, and form detrimental gum deposits. These undesirable changes of a well refined oil may occurwhen the product is being marketed, and make the product unattractive, of

lower value, or even unsalable. The use of dyes to mask the defect of color instability is not always satisfactory, because'the dye does not necessarily correct the deterioration, and the product continues to undergo an undesired change in appearance.

An object of this invention is to provide a method for stabilizing the color of highly refined petroleum hydrocarbon oils which are purified to the extent that they are substantially free of reactive sulfur and meet specification requirements of being non-corrosive in a copper strip corrosion test.

A further object of this invention is to provide purified motor fuel products of increased color stability, with satisfactory freedom from contamination by corrosive substances which render the fuel unsuitable for blending with lead alkyl anti-knock agents and without substantial detriment to their anti-knock values. I

A further object is to provide highly refined water-white petroleum oils of increased color stability and of suificient purity to meet commercial requirements.

I am aware that aryl thiazoles have been proposed as addition agents for use in the vulcanization of rubber, as lubricating oil addition agents for inhibiting corrosion of certain types of bearings, and as corrosion inhibitors in light liquid oils containing constituents corrosive to metals. But in accord nce with the present invention, I

have discovered that in highly refined hydro- ,can be beneficially used in purified motor fuels suitable for improvement with a tetraethyl lead anti-knock agent.

Although rubber and a number of commercial petroleum products such as certain lubricants and fuels permissibly containreactive sulfur to such an extent that these materials are actually corrosive to copper and similar metals, highly refined '40 kind of oil under comparable conditions.

active sulfur harmfully accentuates carbonization' of the wick, while in a leaded fuel it very pronouncedly lowers the anti-detonating effectiveness of the lead alkyl anti-knock agent. To meet these requirements, a motor fuel generally has to be purified both by strong sulfuric acid refining and a sweetening treatment, and as a result of these drastic treatments properly controlled the final products is substantially free of reactive sulfur, such as in the form of elementary sulfur, mercaptan-su1fur, or polysul- The extent to which a light petroleum distillate should be purified before the addition of the mercapto-aryl thiazone color stabilizer has been determined experimentally, and the results show that the reactive sulfur content of the distillate should not exceed 0.004% and preferably should be less than 0.003% by weight, these determinations being made with a mercury number test.

The mercury number is a quantitative measure bottle close to a standardized source of'light so that the opacity of the oil content as increased by the dispersed metallic sulfide can be measured in comparison to the opasity produced by a known concentration of the sulfide in the same The mercury number of an oil varies directly in proportion to the amount of reactive sulfur added to the oil and a unit increase in mercury number is substantially equal to an increase of 0.001%

of reactive sulfur content.

for three hours to the oil at 122 F. or for one hour at 212 F. When the oil fails to satisfactorily pass in these requirements, the color stabilizing effect cannot be satisfactorily obtained with minimal amounts of the thiazole compound, and excessive amounts of the thiazole compound as well as excessive reactive sulfur in the oil considerably reduce the anti-knock value of the motor fuel distillate.

As an example, samples of a cracked gasoline refined to a mercury number of 2 to have a Saybolt color above +20 and satisfactorily pass the copper strip corrosion test for three hours at 122 F. and for one hour at 212 F. were compared with samples of the thus treated gasoline increased in mercury number by addition of 2 mg. of reactive sulfur per 100 ml. for color stabilizing efiects of added stabilizer in the presence and absence of metals. In each test, the same amount of color stabilizer was used, the samples were exposed to the same intensity of light for the same period, and.the proportion improvement in the sunlight stability was observed and recorded to obtam the following data:

Distillate base I Sunlight stability improve- T ment with mercapto-benest M Copper strip zothiazole added in Cone. of

gg? corrosion, 60 1#/l000 bbls. (42 gal.)

u 8 min. at 212 F.

l 2 Passed No metal present... +l8. 7% 2 2 ..do Copper strip present. .+l2. 3 2 0. Iron strip present" +18. 7 4 Above 4. Failed No metal present 0. 5 Above 4 l ..rlo Copper strip present..--l2. 5% 6 Above 4... .....do Iron strip present"... 0.

An aryl thiazole found to possess very desirable properties for use as a color stabilizer for the objects set forth is mercapto-benzothiazole. This compound in very minute amounts functions very effectively to retard discoloration of the, highly purified petroleum products.

To determine the optimum concentrations of the color stabilizer, a series of experiments were conducted with gasoline distillates refined to Saybolt color numbers above +20 and mercury numbers below 4. To the samples were added varied The following example further illustrates the use of mercapto-benzothiazole as a color stabilizer and demonstrates its effectiveness and some of its advantages:

Example A highly purified gasoline which passed the copper strip corrosion test, showing no discoloration of copper with which the oil was kept in contact for a period of three hours at 122 F.. was used as control for a series of tests in which samples of this oil blended with small amounts of mercapto-benzothiazole and combinations of mercapto-benzothiazole with efiicient phenolic gum inhibitors were subjected to sunlight stability tests and cloudiness tests. The concentration of the mercapto-benzothiazole used in each instance was 2.0 pounds per thousand (42 gal.) barrelsoi gasoline which had the following inspection properties:

Gravity, A. P. I 61.8 Doctor Test Pass Copper Strip Corrosion Test, A. S. T. M. Pass Distillation I. B. P F 95 12.0% F 140 18.0% F 158 39.0% ..F.... 212 61.0% F 25'? 80.5% ..F 302 95.0% F 356 F. B. P F 385 ASaybolt colorimeter was used for evaluating the color of the samples. The sunlight stability test was carried out ina manner to give reproductible and comparative results by subjecting the samples contained in sunlight penetrable quartz glass bottles for four hours at 120 F. to

summer sunlight radiations of a sunlight lamp at a fixed intensity. The data on these tests are amounts of the color stabilizer, and each sample 40 given in t following t m Added Final mercapto- Initial Color hold color benzocolor 16 hrs./ (Saybolt) Cloudthiazole, (sa bolt) 212 F. sunlight iness mg./l00 1111. Y (Saybolt) stability test 0 +28 +23 +11 Medium 0.6 +28 +23 +16 Slight. 0 +28 +23 +11 Medium o 0.6 +28 +23 +17 Slight. llilmlk+wood tar phe- 0 +28 +22 +11 Medium D0 0. 6 +28 +24 +18 Slight Blank+amlnophenol 0 +28 +17 +11 Heavy D0 O. 6 +28 +23 +17 None. Blank+benzyl p-ami- 0 +21 +9 +12 Medium.

no phenol.

D0 0.6 +2l +1l +18 None.

was tested for color stability improvement to obtain the following results:

Added mercaptobenzothiazole Sunlight stability Lb 11000 42 Immates. men gal.) bbls.

Percent 0. 0O 0. 0 O. 29 l. 0 +12. 5 0. 58 2. 0 +18. 7 1. l6 4. 0 +25. 0 2. 32 8. 0 +18. 7

Thus. it is to be observed that the optimum improvement is obtained with about 1 mg. of the thiazole compound per 100 ml. of the oil, and that the concentration of the color stabilizer should preferably have a minimum of about 0.2 mg. and a maximum of about 2.5 mg. per 100 ml. of the oil.

It is to be observed that the samples containing mercapto-benzothiazole have improved color stability of from 2 to 7 Saybolt color numbers in the color hold test and from 5 to 7 numbers in the sunlight stability test, and further, that these samples had substantially complete elimination of cloudiness, particularly when phenolic gum inhibitors were also present.

The gum inhibitors, in general, are indispensable particularly for cracked products and motor fuels blended with lead alkyl anti-detonating agents for avoidance of undesirable gum deposition. The phenolic gum inhibitors as a class, include various alkylated phenols, petroleum phenols, wood tar phenols, and amino phenols, are among the most efficient and are used in concentrations ranging from about 0.001% to 2% or more by weight of the fuel. These gum inhibiting compounds, however, have a bad fault of lowering the color hold of a fuel, which is the color stability of the fuel over a long period of heating, and furthermore they do not make any improvement in the sunlight color stability of the fuel. As demonstrated by the foregoing test data, the thiazole color stabilizer effectively acts to correct the color stability of the fuel with the gum inhibitor present by improving the color hold, sunlight stability, and even in greatly diminishing the cloudiness of the fuel.

Oils with improved sunlight stability obtained in accordance with the present invention do not discolor noticeably to the naked eye when exposed to the intensified sunlight radiations for a period of four hours in a four ounce glass bottle.

In the purified oils having a sufficiently reduced concentration of reactive sulfur and containing an' effective amount of the color stabilizing agent, various colorizing dyes are also very satisfactorily used. Oil-soluble dyes can thus be protected from undergoing changes normally caused by the action of sunlight or color forming bodies in the oil. For example, various centration, minimal optimum amounts of about 0.2 to 1 mg. per 100 m1. of oil are preferred. In these proportions, the aryl thiazoles are completely soluble in the hydrocarbon oil and do not have any appreciable adverse efiects on a purified motor fuel containing a lead alkyl anti-knock agent.

This invention is not to be limited by any theory, nor by the examples given as illustrations.

I claim:

1. The method of stabilizing the color of a light petroleum distillate oil which comprises highly refining said oil to the extent that it satisfactorily passes the A. S. T. M. copper strip corrosion test conducted for one hour at 212 F. by a reduction of its reactive sulfur content to less than 0.004% and has a Saybolt color above +20, and thereafter adding to the thus refined oil a small amount of an aryl thiazole compound to act as a color stabilizer in a proportion of at least about 0.2 mg. per 100 m1. of the oil.

amino base dyes may be used in amounts of 0.005% to 0.1% by weight of the oil including compounds of the type of oxazines, indophenols indamines, eurhodines, safranines, and amino azo base dyes.

In place of mercapto benzothiazole or together therewith, other closely related aryl thiazole compounds may be used as the color stabilizing agent. These compounds are, in general, characterized by an aromatic nucleus of which ortho carbon atoms are linked to nitrogen and sulfur in a thiazole group as shown in the following structural formula:

in which R is .preferably a mercapto group, but may be hydrogen, a hydrocarbon group, a hydroxy group, or a hydrocarbon radical with a thio linkage to the carbon in the thiazole group. Other specific examples of this type of compound are alkaryl 'thiazoles, such as mercapto isopropyl benzothiazole and mercapto isoamyl benzothiazole.

Also, other substituents may be present in the aromatic nucleus such as amino, hydroxyl, or chloro groups.

To obtain the desired effects of the color stabilizing agent, it may be used in concentrations ranging from 0.2 to 2 mg. per 100 ml. of the oil.

But as the efiectiveness'of these compounds does not increase exactly in proportion to their con- 2. The method of stabilizing the color of a petroleum motor fuel containing cracked hydrocarbons boiling in the gasoline boiling range and components which normally tend to develop objectionable color on exposure to sunlight, which comprises refining said fuel to the extent that it satisfactorily passes the doctor test and the A. S. T. M. copper strip corrosion test conducted for one hour at 212 F. by reduction of corrosion inducing reactive sulfur in the fuel to less than 0.004%, then blending with the thus refined fuel a small amount of mercapto benzothiazole in a proportion of at least about 0.2 mg. per ml. of the fuel to improve the color stability of the 3. A color stabilized petroleum gasoline comprising a highly purified petroleum gasoline fraction refined to eliminate the corrosive components therein so that the gasoline satisfactorily passes the A. S. T. M. copper strip corrosion test conducted for one hour at 212 "F. and to which is added a small amount of a phenolic gum inhibitor and a small amount of an aryl thiazole compound for efiecting color stabilization including a diminution of cloudiness.

4. A color stabilized petroleum gasoline as described in claim 3, in which the phenolic gum inhibitor is an amino phenolic compound, and the added aryl thiazole compound substantially improves the color hold of the gasoline.

5. A color stabilized petroleum gasoline in accordance with claim 3, in which said aryl thiazole compound is mercapto benzothiazole.

HENRY C. PAULSEN. 

